As the present trend in tire-making technology continues toward the use of higher silica loadings in rubber compounds, there is a challenge to contain levels of environmentally released alcohol as a volatile organic compound (VOC) during compounding, processing, curing and storage of silica-reinforced rubber compounds.
In our U.S. patent application Ser. No. 11/387,569, filed Mar. 23, 2006, entitled “Compounding Silica-Reinforced Rubber With Low Volatile Organic Compound (VOC) Emission,” the entire disclosure of which is hereby incorporated by reference, we describe the preparation of alkoxy-modified silsesquioxane (AMS) compounds and co-alkoxy-modified silsesquioxane (co-AMS) compounds that generate less alcohol than conventional alkoxysilane-containing silica-coupling and/or silica dispersing agents used in rubber compounding. The decreased amount of alcohol produced when using the AMS and co-AMS compounds potentially results in vulcanized rubber compounds having one or more improved properties such as, but not limited to, enhanced rubber reinforcement, increased polymer-filler interaction and lower compound viscosity, providing for tires having improved wet and snow traction, lower rolling resistance and decreased hysteresis.
An exemplary co-AMS disclosed in the aforementioned patent application is a blocked-mercapto AMS. As disclosed therein, a blocked-mercapto AMS may be produced by the co-hydrolysis and co-condensation of an alkyltrialkoxysilane or an alkyltrichlorosilane with, for example, a blocked-mercaptoalkyltrialkoxysilane. Another blocked-mercapto AMS disclosed therein is an acetyl-blocked-mercapto AMS. The acetyl blocking group can be introduced, for example, by reacting thioacetic acid with an AMS produced from alkyltrichlorosilane reactants. However, care must be taken to avoid a pH above 7 for any length of time during the reaction to avoid gelled AMS.
Novel and non-obvious alternative methods of synthesizing blocked-mercapto AMS compounds are provided herein. Moreover, an alternative method for introducing an acetyl blocking group on an AMS compound is provided.